Eastern Tent Caterpillars

May 19, 2016 – Kenosha News

Question: There is a mass of webbing in the forks of the branches of my crab apple tree. What could this be? A. K.

Eastern tent caterpillar webbingAnswer: In spring, the eastern tent caterpillar sets up camp in tree canopies, most often in fruit trees, like apple, plum, and flowering crabapples. The tent of white webbing is easier to identify than the actual hairy black, white and yellow striped, blue spotted caterpillar itself.

The tent offers the caterpillars protection from predators and from temperature extremes, and it will become larger and larger as the caterpillars continue to grow. The caterpillars leave the tent (nest) to feed on newly emerged foliage in early morning, in the evening, or at night. Rainy or cold weather as well as the intense afternoon sun keep them huddled within their webbed wigwams.

They overwinter as eggs, massed around small branches and look as if they have traded in their silken cover for a shiny, black tubular tupik. The larvae hatch around the time of bud break with caterpillars from the same egg mass forming a colony. Larger colonies form when two or more egg masses unite. When finished feeding, they leave their namesake nest and spin white/yellow cocoons on tree trunks, fences, or other structures. Reddish brown adult moths emerge within a few weeks. Eggs laid on small branches by these adult moths will repeat the cycle next spring.

Eastern tent caterpillars rarely kill trees, yet serious defoliation of a tree can result with a heavy infestation. Healthy trees usually leaf out again within a few weeks of being defoliated. Considered a nuisance, most of the damage by these voracious creatures is basically cosmetic.

To control these pests if they have camped out on your grounds, remove the tents in spring with gloved hands (if they are within reach). Larger webs or webs beyond reach can be removed using a stick or tool handle. Grab as much of the web as possible along with any caterpillars, which can be crushed, buried, or burned. Refrain from attempting to burn tents in trees since this may damage the trees to a higher degree than the caterpillars. To control in winter, locate and destroy egg masses by pruning out the affected branches or apply dormant oil sprays to the egg masses to suffocate the eggs. A natural insecticide, Bacillus thuringiensis var. kurstaki (Bt), can be applied to caterpillars while they are still young, but it is difficult to apply to them while tucked in tents.


Kenosha County UW-Extension LogoJeanne Hilinske-Christensen, M.S., is the Consumer Horticulture Educator for Kenosha County UW-Extension.